Material working apparatus having an electromagnetically vibrated working tool

ABSTRACT

A material working apparatus having an electromagnetically vibrated working means, particularly an ultra sonic dental apparatus having a vibrated dental tool, wherein the magnitude of the vibrations is adjustable by hand on the apparatus itself.

D United States Patent 11 1 [111 3,763,41 1 Goof 1 Oct. 2, 1973 MATERIAL WORKING APPARATUS [56] References Cited H33VIN'EEAN ELEIEFROMAGNETICALLY UNITED STATES PATENTS v RA D wok NG TOOL 3,691,437 9/1972 Andersson et a1. 318/118 [76] Inventor: Sven Karl Lennart Goof, G'ammel 3,694,713 9/1972 Duren et a1 1 318/118 X Strandvj 236 A, Humlebaek, 1,019,213 3/1912 Adams 310/30 Denmark 3,526,036 9 1970 Goof 32/58 x 1,164,475 [2/1915 Croston 318/122 [22] Fllfid; Mar. 27, 1972 427,070 5/1890 Gibbs 3l0/30 211 App]. No.: 238,085

Primary Examiner-D. F. Duggan I AttorneyRobert D. Flynn et a]. [30] Forelgn Appllcatlon Priority Data M 21,1971 D k 1527 57 ABSTRACT Cl A material working apparatus having an electromag- I 4 netically vibrated working means, particularly an ultra [51] Int. Cl .Q H011! 9/00 sonic dental apparatus having a vibrated dental tool, Field of Search wherein the magnitude of the vibrations is adjustable 310/26, 8.1, 30, 39, 35; 32/DlG. 3, DIG. 4, 58, 53, 78; Sl/DIG. ll, 59, 55

by hand on the apparatus itself.

21 Claims, 9 Drawing Figures BJESAR l akented Oct 2, 1973 2 Sheets-$heet .1

MATERIAL WORKING APPARATUS HAVING AN ELECTROMAGNETICALLY VIBRATED WORKING TOOL The present invention relates to a material working apparatus having a hand piece structure containing a adapted for transferring ultra sonic vibrations to a material working tool, such as a dental tool.

Ultra sonic working apparatuses of this type are used by dentists for mechanical removal of dental films. Such an apparatus is for instance disclosed in German Offenlegungsschrift Pat. No. 1,916,507.

In this apparatus of the prior art current is switched on and off by means of a movable ring member on the apparatus.

In this and other known apparatuses for ultra sonic treatment of teeth the dentist must in order to adjust the vibrations of the dental tool operate a control button or knob of a control box, wherein the various electrical components for feeding and transforming the current are placed. This control box will usually be hung either on the pillar which forms part of the dental chair, and a.o. carries the dentists drills and drilling tools, which has the disadvantage that the dentist only with difficulty can regulate said control button without disturbing the patient, or said control box may be hung on a wall in the clinic or placed on another table, which in such case requires room in the clinic. In any case the dentist must in order to regulate said control button remove himself from his position over the patient and this will at least delay his work. Adjustment of said control button is often necessary during treatment of a patient because the patient may have various types of dental films which require different vibrations of the dental tool. The tip of the dental tool generally describes an elliptical course, and when hereinbefore vibrations of the dental tool have been mentioned there is meant the magnitude or extension of the elliptical course. For simplicity the vibration will hereinafter be referred to as the amplitude.

In view of the problems discussed above it will be realized that there is a need for a further simplification of the regulation means in order to avoid that the amplitude of the dental tool shall be adjusted by means of'a control button or knob on said control box.

According to the present invention there is provided a material working apparatus of the type briefly referred to above, and wherein the improvement or the characteristicfeature is an electrically conducting device placed withinthe magnetic field of the coil and being adapted for gradually and controllably decreasing the strength of the magnetic field through the core.

By decreasing the strength of the magnetic field through the core it is possible to decrease the amplitude of the working tip from a predetermined maximum value corresponding to the greatest amplitude which is practically necessary for removal of dental films, to a lower value corresponding to the smaller working requirements when the films are easier to remove. Said maximum value of the amplitude may correspond to the optimal value which is determined by the electrical components of the control box with regard to the desired frequency, which in general may be of the order of to 50 kilohertz. In other words the apparatus may be elaborated in such a way that there is a minimum loss of power when the strength of the magnetic field through the core is not reduced, and when it is reduced the loss of power will be reflected as heat. The transducer coil which also may be considered as a primary coil induces a current in said electrically conducting device, which in the same terms also may be considered as a secondary coil, and by adjusting said electrically conducting device it is possible to amend the resulting magnetic field through the core.

The positioning of the electrically conducting device may in several ways, of which some preferred are discussed hereinafter, be made by hand on the apparatus itself, whereby the disadvantages of the prior art referred to above have been avoided.

In a preferred embodiment of the invention the electrically conducting device is a short-circuited or shortcircuitable coil preferably having adjustable electrical conductivity.

In this embodiment it is preferred that the electrically conducting device comprises a first portion and a second portion, said first and second portions being electrically connectable and each consisting of electrically conducting material, said first portion comprising two contacting means defining there between a slot extending in the longitudinal direction of the hand piece structure, said two contacting means being connected with each other along at least a part of their length by means of an electrically conducting connecting means extending round the core without passing said slot, and that said second portion is mounted and elaborated in such a way that a relative movement of said two portions under electrical connection of the two contacting means places said second portion so that it covers increasing lengths of said slot in said first portion.

Said second portion may in a further embodiment be an electrically conducting cylinder part of varying height, said cylinder part being adapted for covering increasing lengths of said slot by relative movement in proportion to said first portion. When the term cylinder part is used there is meant any part of a cylinder, i.e., a body in which a cross section perpendicular to a generatrix is a circle or a segment of a circle.

Preferably the cylinder part is mounted for sliding in contact with the other portion of the electrically conducting device.

The greatest height of the cylinder part may be essentially equal to the length of the slot, whereby the length of the electrically conducting device is minimized.

According to the invention one of the portions of the electrically conducting device may be secured to the hand piece structure and be rotatable with at least a part thereof, whereas the other portion is secured unrotatably inside of said one portion. This embodiment facilitates regulation of the two portions from the outside. In regard of the construction of the other parts of the apparatus it is preferred that it is the cylinder part of varying height which is secured to the hand piece structure.

In another embodiment of the invention said second portion of the electrically conducting device comprises an elongated member of a width corresponding to the width of said slot, and wherein said two portions can be axially displaced in proportion to each other under electrical connection of said two contacting means so as to cover increasing lengths of said slot in said first portion. Hereby said first portion may be stationary, and said elongatedmember may be axially displacable in the longitudinal direction of the hand piece structure.

The first portion of the electrically conducting device comprises as stated above two contacting means, which are connected with each other along at least a part of their length by means of an electrically conducting connecting means extending round the core without passing the slot. When the connecting means connects the two contacting means over their full length the first portion may be a slotted cylinder.

When the strength of the magnetic field through the core is reduced in the meaning described above heat is developed in the electrically conducting device, and this may be inconvenient for the dentist.

In the most preferred embodiment of the invention this disadvantage has been overcome by connectinG only two adjacent ends of the contacting means by means of the connecting means, the latter in such case being a slotted cylinder, and in which embodiment the second portion is mounted only at the non-connected part of the contacting means. Hereby a part of the heat can be displaced through the connecting means which can be placed in a position where it does not interfere with the operating of the apparatus. Most convenient the connecting means has greater electrical resistance than the contacting means so that the major portion of the heat developed is removed to the connecting means. For example the contacting means may consist of pure silver and the connecting means may consist of electrolyte nickel, phosphor bronze or platinum. In order to avoid corrosion suitable sealings may be provided which prevent introduction of moist.

' In dental tool apparatuses of the type described in the present specification a cooling medium usually flows through a mantel enclosing the transducer coil and core, and by mounting the connecting means of the first portion in a recess in said mantel it is easier to remove the heat developed by means of the cooling medium.

The invention will now be described with reference to the accompanying drawings illustrating preferred embodiments thereof, in which FIG. I is a perspective view of the apparatus,

FIG. 2 isan exploded view of the apparatus shown in FIG. 1 illustrating one embodiment,

FIG. 3 is a schematic view showing the electrically conducting device of FIG. 2,

FIG. 4 is a schematic view of another embodiment of the electrically conducting device,

FIG. 5 is a further embodiment of the electrically conducting device,

FIG. 6 is a still further embodiment of the electrically conducting device,

FIG. 7 is an-exploded view similar to that of FIG. 2, but showing the most preferred embodiment of the electrically conducting device,

FIG. 8 is a schematic view of the electrically conducting device in the apparatus of FIG. 7, and

FIG. 9 is a schematic view of a still further embodiment of the electrically conducting device.

Referring more particularly to the drawings, wherein like reference characters designate like or corresponding parts throughout the different views, and referring particularly to FIGS. 1, 2 and 3 the numeral 10 generally designates an ultra sonic dental apparatus. The apparatus comprises a tip 12 mounted in a tip structure (not shown), which by means of a high frequency current through a conduit 14 is able to perform high frequency vibrations. The way in which the current is transferred into vibrations of the tip is generally known in the art, in which connection reference is made to the above mentioned German Offenlegungsschrift. The transformation of current into mechanical vibrations does not form part of the present invention, and a further description at this matter is therefore deemed unecessary. For washing away the film material which is removed from the tooth and for cooling of the apparatus there is provided a cooling medium supply pipe 16, which also may be fed through the conduit 14. The way in which the water flows from the conduit 14 to the pipe 16 does not form part of the present invention, but may take place for instance as explained in the specification of the above mentioned German Offenlegungsschrift. The tip 12 and the pipe or duct 16 are mounted in a connecting means 18 whereto also the transducer core 20 (FIG. 2) is secured. The part of the apparatus which just has been described is removably mounted in a retention means 22, and the whole structure is inserted in the remaining part of the apparatus which includes a hand piece structure 24 of general cylindrical form so that it is easy to grip. The numeral 26 designates an axially movable ring member 26 which through a flat bar 28 can control a micro switch (not shown) in the rear end of the apparatus. The micro switch will normally be switched off in the position of the ring member 26 shown in FIG. I and by moving said ring to the rear until it reaches a circular edge 30 the micro switch is switched on. A current will now pass through a coil 32 whereby the core 20 will perform longitudinal vibrations with a frequency corresponding to the frequency of the current. The electrically conducting device according to the invention is denoted by reference numeral 40 in FIG. 3 and comprises a first portion 42 and a second portion 44. The first portion 42 is elaborated as a slotted cylinder defining a slot with parallel sides. The edge parts of the portion 42 facing the slot are turned down and retained in grooves in a tubular member 46 (FIG. 2) mounted on the outside of the coil 32 and also having an extended slot for receiving and guiding the bar 28 for controlling the micro switch. The second portion 44 comprises as shown in FIG. 2 a cylinder part having a straight base 48. The cylinder part has varying height with the greatest height along the side 50 and the smallest height along the other side 52. The length of the side 52 can fall against zerocorresponding to that the cylinder part has a sharp corner. Opposite the base 48 the edge 54 is parallel to the basis at the end of the side 50 and the edge 54 is of approximately the same length as the width of the slot in the portion 42. FIG. 3 shows the relative mounting of the portions 42 and 44. In the position shown in FIG. 3 approximately five-sixths of the length of the slot is covered by the portion 44. By turning the portion 44 counterclockwise the part of the slot which is covered by the portion 44 is increased, and when the side 50 aligns with the edge 62 of the portion 42 the slot will be almost completely covered. Turning of the portion 44 clockwise reduces that part of the slot which is covered by the portion 44 until the side 52 is beyond the slot edge 62 in which position the device 42 has no essential influence on the magnetic field through the core. In the embodiment shown in FIG. 3 the two portions 42 and 44 slide in electrical contact with each other.

When the portion 42 is secured to the tubular member 46 the second portion 44 may be secured to a rotatable part 56 of the hand piece structure 24. Securing of the two portions 42 and 44 may be obtained in conventional way, for example by gluing. On the inner side of the rotatable hand piece part 56 there can be provided a stop means 58 as best seen in FIG. 2. The stop means 58 abuts by actual rotation the bar 28. In connection with the stop means 58 or in another suitable way an indicator 6!) may be provided. The indicator corresponds with a scale as indicated by the FIGS. 11, 2, 3, 4 the lowest number corresponding to the smallest amplitude of the vibrating tool 12. By turning the rotatable hand piece part 56 clockwise, i.e., towards higher figures, the influence on the strength of the magnetic field through the core is reduced, and increasing amplitudes are obtained for the tool 12. The portions 42 and 44 are electrically conducting at least on the surfaces which slide against each other, and preferably they are made from an electrically conducting material, such as phosphor bronze. No essential thicknessis required, and the portions 42 and 44 may be films or sheets.

FIG. 4 is a schematic segment corresponding to that of FIG. 3, but showing a different embodiment for the electrically conducting device generally designated 70. The device 70 comprises a longitudinally slotted cylinder 72 and an elongated member 74. The cylinder 72 may be secured to a tubular member in a similar way as the portion 42 to the member 46 of FIG. 2. The cylinder 72 may similarly consist of a film of for example phosphor bronze. The elongated member 74 comprises an elongated part 76 of a width corresponding to the width of the slot in the cylinder 72, and the elongated part 76 is secured to a guiding member 78 which may slide on the outer surface of the hand piece in an apparatus similar to that shown in FIG. 1. By means of a scale from 1 to for example 5 the elongated member 74 can be adjusted to a desired reduction of the strength of the magnetic field through the core 20. In the position shown in FIG. 4 there will only be a little change in the magnetic field through the core, but by moving the member 74 towards right of the drawing the total conductivity of the device 70 is increased and when the member 74 reaches a position wherein the part 76 covers the slot 49 completely the greatest reduction of the strength of the magnetic field will be obtained.

In the embodiment shown in FIG. 5 the electrically conducting device is a ring member 80, which can be axially displaced in two directions on a portion 82 of the hand piece 24 having reduced diameter. By displacing the device 80 towards right from the position shown in the drawing, La. towards increasing scale figures as shown on the hand piece portion 82, the influence on the magnetic field through the core will fall and accordingly the tip of the working tool will vibrate with increasing amplitude.

In the embodiment shown in FIG. 6, which is a segment similar to that shown in FIGS. 3 and 4, the electrically conducting device 90 comprises a sliding contact on the coil 32. The corresponding surface of the coil 32 has no electrical isolation and by displacing the sliding contact in the axial direction two or more windings of the coil will be short-circuited, and the effect will also in this case be a change in the strength of the magnetic field through the core 20.

Referring now to FIGS. 7 and 8 there is shown the most preferred embodiment of the apparatus according to the invention. The electrically conducting device generally designated 40' (FIG. 3) comprises a first portion 42' and a second portion 44. The first portion 42' is comprised of two contacting meanS 43,45 and a connecting means 47. Between the contact means 43,45 there is defined an axially extending elongated slot 49. The contacting means 43,45 are here shown as two similar plates of general rectangular shape, but they may have any desirable shape which does not have to be the same for the two contacting means, and in regard of their relative position the only requirement is that they define a slot. A part of the length of the contacting means are connected with each other by means of the connecting means 47 which in the embodiment shown is a slotted cylinder which is secured to a circumferential recess in the turbular member 46. Inside the tubular member 46 a cooling medium, such as water, may flow, for instance in the way taught in the above mentioned German Offenlegungsschrift. The contacting means 43,45 and the connecting means 47 may be integral with each other and consist of a material, such as phosphor bronze, but are preferably as sug gested in the drawing three individual parts, whereby the connecting means may consist of a material having greater electrical resistance than the contacting means. The second portion 44' of the device 40' is a cylinder part similar to that shown by 44 is FIGS. 2 and 3. By turning the portion 44 counterclockwise an increaslng part of the slot 49 is covered by the portion 44 which slides in electrical contact with the contacting means 43 and 45. When the side 50 is aligned with the edge 62' of the portion 42' the slot will be almost completely covered. By turning the portion 44' clockwise the part of the slot which is covered by the portion 44' is reduced until the side 52 is beyond the edge 62' of the slot. It will be realized that the device shown in FIGS. 7 and 8 is similar to that shown in FIGS. 2 and 3 as far as amendment of the strength of the magnetic field of the core 20 is concerned. I

When the magnetic field is reduced heat is developed in the electrically conducting device, and in the embodiment shown in FIGS. 2 and 3 it will be realized that the heat is developed at the place where the dentist naturally will grip the apparatus. This may be inconvenient and in the embodiment shown in FIGS. 7 and 3 it is possible to remove the heat through the connecting means 47 to the cooling medium flowing inside the tubular member 46.

' In the embodiment shown in FIG. 9 the electrically conducting device comprises an elongated member 74' which is similar to the elongated member 75 shown in FIG. 4, as well as a portion 72' which is similar to the portion 42 discussed with reference to FIGS. 2 and 3. The device of FIG. 9 acts in the same way as the device of FIG. 4 as regards change in the magnetic field of the core 20, and reference is therefore made to the description given in connection with FIG. 4. Furthermore it provides the same advantages as the embodiment shown in FIGS. 7 and 3 in respect of removal of heat developed when the magnetic field of the core 20 is changed.

Although the invention has been described in connection with some preferred embodiments, it will be appreciated that many amendments are possible within the scope of the invention as defined in the appended claims. For example the electrically conducting device may in a suitable way be mounted between the core 20 and the coil 32, and the conductivity of the electrically conducting device may be varied in several ways, for example by substituting the elongated members of FIGS. 4 and 9 by a resilient means which by depression may cover varying lengths of the slot 49.

Finally it is remarked that FIGS. 3 to 6, 8 and 9 only are schematic views of parts of an apparatus having an electro magnetically vibrated working means, which may be of any type not limited to dental tools.

. I claim:

1. Ultrasonic vibratory machining apparatus having a hollow handpiece structure and a transducer mounted therein, said transducer comprising a core surrounded by a transducer coil, said transducer being adapted to excite high frequency vibrations in a machining tool which is rigidly secured to said core when said transducer coil is energized by an alternating high frequency current to create a magnetic field, the improvement comprising: an electrically conducting device having a movable element mounted within the magnetic field of said transducer coil when energized, said movable element being operable from said handpiece structure so as to gradually control the strength of the magnetic field through said core, whereby the deflections of the vibrating machining tool are correspondingly gradually controlled.

2. The apparatus of claim 1, wherein the electrically conducting device includes a movable member in contact with the transducer coil such that at least two windings thereof are connected with each other by said conducting device.

3. The apparatus of claim 1 wherein the electrically conducting device comprises a single short-circuitable coil.

4. The apparatus of claim 1, wherein said electrically conducting device is a shiftable member in electrically conducting contact with the windings of said transducer coil and being adapted to short-circuit an increasing number of windings during its shifting in one direction.

5. The apparatus of claim 1, wherein the electrically conducting device comprises a short-circuited coil.

6. The apparatus of claim 2, including means for adjusting the conductivity of the short-circuited coil.

7. The apparatus of claim 6, including means for adjusting the conductivity of the short-circuitable coil.

8. The apparatus of claim 5, wherein the electrically conducting device comprises a ring member of electrically conducting material which is displaceable in the longitudinal direction of said hand piece structure.

9. The apparatus of claim 1, wherein the electrically conducting device comprises a first portion and a second portion, said first and second portions being electrically connectable, and each being comprised of electrically conducting material, said first portion comprising two contacting means defining therebetween a slot extending in the longitudinal direction of the hand piece structure, said two contacting means being connected with each other along at least a part of their length by means of an electrically conducting connecting means extending round the core without passing said slot, and said second portion being mounted in electrical contact with said two contacting means of said first portion such that a relative movement of said first and second portions causes said second portion to cover increasing lengths of said slot in said first portion.

10. The apparatus of claim 9, wherein said second portion includes an electrically conducting cylinder part having varying height, said cylinder part being adapted for covering increasing lengths of said slot by relative movement in proportion to said first portion.

11. The apparatus of claim 10, wherein the greatest height of said cylinder part is essentially equal to the length of said slot.

12. The apparatus of claim 10, wherein one of said portions is secured to the hand piece structure and rotatable with at least a part thereof, and the other portion is secured non-rotatably inside of said one portion.

13. The apparatus of claim 12, wherein the portion which is secured to said hand piece structure is said second portion.

14. The apparatus of claim 9, wherein said second portion comprises an elongated member having a width corresponding to the width of said slot, and said two portions are axially displaced in proportion to each other under electrical connection of said two contacting means so as to cover increasing lengths of said slot in said first portion.

15. The apparatus of claim 14, wherein said first portion is stationary, and said elongated member is axially displacable in the longitudinal direction of the hand piece structure.

16. The apparatus of claim 9, wherein said first portion comprises a slotted cylinder, said contacting means being integral with the connecting means.

17. The apparatus of claim 9 wherein the connecting means of said first portion is a slotted cylinder which only connects two adjacent ends of the contacting means, said second portion being mounted only at the nonconnected part of the contacting means.

18. The apparatus of claim 17, wherein the connected ends of the contacting means are those that are most remote from the material working tool.

19. The apparatus of claim 18, wherein the connecting means has greater electrical resistance than the contacting means.

20. The apparatus of claim 9, wherein the electrically conducting device is mounted on that side of the transducer coil which is opposite the side on which the transducer core is mounted.

21. The apparatus of claim 9, wherein the transducer coil and core are enclosed in a mantel through which a coolant can be passed, and wherein said connecting means of said first portion is mounted in a recess in said mantel.

# t t t '3 

1. Ultrasonic vibratory machining apparatus having a hollow handpiece structure and a transducer mounted therein, said transducer comprising a core surrounded by a transducer coil, said transducer being adapted to excite high frequency vibrations in a machining tool which is rigidly secured to said core when said transducer coil is energized by an alternating high frequency current to create a magnetic field, the improvement comprising: an electrically conducting device having a movable element mounted within the magnetic field of said transducer coil when energized, said movable element being operable from said handpiece structure so as to gradually control the strength of the magnetic field through said core, whereby the deflections of the vibrating machining tool are correspondingly gradually controlled.
 2. The apparatus of claim 1, wherein the electrically conducting device includes a movable member in contact with the transducer coil such that at least two windings thereof are connected with each other by said conducting device.
 3. The apparatus of claim 1 wherein the electrically conducting device comprises a single short-circuitable coil.
 4. The apparatus of claim 1, wherein said electrically conducting device is a shiftable member in electrically conducting contact with the windings of said transducer coil and being adapted to short-circuit an increasing number of windings during its shifting in one direction.
 5. The apparatus of claim 1, wherein the electrically conducting device comprises a short-circuited coil.
 6. The apparatus of claim 2, including means for adjusting the conductivity of the short-circuited coil.
 7. The apparatus of cLaim 6, including means for adjusting the conductivity of the short-circuitable coil.
 8. The apparatus of claim 5, wherein the electrically conducting device comprises a ring member of electrically conducting material which is displaceable in the longitudinal direction of said hand piece structure.
 9. The apparatus of claim 1, wherein the electrically conducting device comprises a first portion and a second portion, said first and second portions being electrically connectable, and each being comprised of electrically conducting material, said first portion comprising two contacting means defining therebetween a slot extending in the longitudinal direction of the hand piece structure, said two contacting means being connected with each other along at least a part of their length by means of an electrically conducting connecting means extending round the core without passing said slot, and said second portion being mounted in electrical contact with said two contacting means of said first portion such that a relative movement of said first and second portions causes said second portion to cover increasing lengths of said slot in said first portion.
 10. The apparatus of claim 9, wherein said second portion includes an electrically conducting cylinder part having varying height, said cylinder part being adapted for covering increasing lengths of said slot by relative movement in proportion to said first portion.
 11. The apparatus of claim 10, wherein the greatest height of said cylinder part is essentially equal to the length of said slot.
 12. The apparatus of claim 10, wherein one of said portions is secured to the hand piece structure and rotatable with at least a part thereof, and the other portion is secured non-rotatably inside of said one portion.
 13. The apparatus of claim 12, wherein the portion which is secured to said hand piece structure is said second portion.
 14. The apparatus of claim 9, wherein said second portion comprises an elongated member having a width corresponding to the width of said slot, and said two portions are axially displaced in proportion to each other under electrical connection of said two contacting means so as to cover increasing lengths of said slot in said first portion.
 15. The apparatus of claim 14, wherein said first portion is stationary, and said elongated member is axially displacable in the longitudinal direction of the hand piece structure.
 16. The apparatus of claim 9, wherein said first portion comprises a slotted cylinder, said contacting means being integral with the connecting means.
 17. The apparatus of claim 9 wherein the connecting means of said first portion is a slotted cylinder which only connects two adjacent ends of the contacting means, said second portion being mounted only at the nonconnected part of the contacting means.
 18. The apparatus of claim 17, wherein the connected ends of the contacting means are those that are most remote from the material working tool.
 19. The apparatus of claim 18, wherein the connecting means has greater electrical resistance than the contacting means.
 20. The apparatus of claim 9, wherein the electrically conducting device is mounted on that side of the transducer coil which is opposite the side on which the transducer core is mounted.
 21. The apparatus of claim 9, wherein the transducer coil and core are enclosed in a mantel through which a coolant can be passed, and wherein said connecting means of said first portion is mounted in a recess in said mantel. 